It is okay to let the prop spin on the saildrive
. Other than a little extra wear on the moving parts
due to the extra "running" time it does not cause problems. For a one time only trip I put a fixed prop on and let it spin. It did start to get a bit loud above 7 knots and when we where in the teens you really knew it was there. I was worried that if I put it in gear
it would turn my small (17hp) engine
over at the higher speeds. I do remember I got 7 knots at WOT (2700) and 6 at cruising rpm
(2000) with that fixed prop.